Absorbent structure in an absorbent article

ABSTRACT

An absorbent structure comprising a silicone foam having pore walls and a plurality of hydrophilic particles anchored to the pore walls of the foam. Some of the hydrophilic particles have an anchored portion firmly anchored to the pore walls and an exposed portion extending outwardly away from the pore walls upon which the anchored portion is secured.

This application is a continuation of U.S. application Ser. No.11/979,758 filed on Nov. 8, 2007, which claims the benefit of priorityfrom U.S. provisional application No. 60/858,371, filed on Nov. 13,2006.

FIELD OF THE INVENTION

The present invention relates to a monolithic absorbent structure havinga facing layer for use in an absorbent article such as a wound dressing,hygiene product, prosthetic device or orthopedic device. Moreparticularly, the absorbent article includes a silicone foam havingpores and a plurality of hydrophilic particles anchored to the porewalls of the foam.

BACKGROUND

Occlusive or moisture-retentive dressings have gained increasingacceptance in treating wounds, in particular pressure sores and ulcers.A wide variety of types of structures are known in the art for use in oras wound dressings, and generally comprise components for receiving,absorbing and retaining exudate. Typically, these dressings includepolymeric foams, polymeric films, particulate and fibrous polymers,hydrogels and hydrocolloids. Dressings with at least one of thesecomponents promote wound healing by providing a moist environment, whileremoving excess exudate and toxic components, and further serve as abarrier to protect the wound from secondary bacterial infection. Whilethese known dressings can effectively manage a wound, many have beenfound to possess certain limitations or disadvantages.

Many known dressings possess the disadvantage of relying solely on apressure sensitive adhesive layer to secure the dressing to skin. Anexample of an adhesive is an acrylate glue. While indeed an acrylateglue securely maintains a dressing over a wound, the glue has a tendencyto strip the central portion of the dressing from the wound and thus maydamage healing tissue.

Many of the known dressings have an absorbent layer that compriseshydrophilic polymeric foam. Unfortunately, many hydrophilic polymericfoam dressings possess the disadvantage of being limited in the amountof exudate that may be absorbed. The limit in exudate absorption of thefoam is often directly related to its overall geometrical size prior toabsorbing a fluid. Typically, hydrophilic foams may expand only to10-20% of their original size.

Another disadvantage to hydrophilic foam dressings is that a certainamount of exudate can be “squeezed” out of the foam due to poor liquidretention. The ability of exudates to be squeezed from the foam, andthus the dressing itself, poses a risk of infection and may interferewith the healing of the wound.

Yet another disadvantage with known foam dressings is that absorption ofexudate by an absorptive layer, such as foam, in contact with the woundcauses the central portion of the applied dressing to swell and push upagainst the wound. Continued swelling can induce separation of the skinadherent layer from the skin outside the wound area, especially at theborder of the wound dressing whereat a “curling” effect may occur. Thisexcessive swelling of the dressing may further lead to leakage of theexudate from the periphery of the dressing, thereby providing a tractfor the invasion of pathogenic microorganisms and promoting macerationof the wound site.

Still another disadvantage of hydrophilic foam dressings is that, ascellular tissue grows during the healing process, the cellular tissuemay firmly bind to the wound dressing. This is especially the case whenthe foam dressing has a coarse and porous exterior surface into whichcellular tissue will grow. Removing the wound dressing when it isadhered to the wound in this manner will likely traumatize the wound andcause additional pain to the patient. Repeated changing of the wounddressing will result in repeated traumatization of the wound and willultimately increase the time needed for the wound to completely heal.

For the foregoing reasons, there is a demand for an absorbent structurewhich prevents wound trauma upon repeated dressing changes, improves thedurability and lifetime of the dressing, anatomically conforms to a bodyportion bearing a wound, possesses suitable fluid uptake, retention andremoval properties, and can be securely maintained on a patient's body.It is also desirous to provide an absorbent structure that has suitableabsorption properties while dispensing with the need to secure a skinadherent facing layer to the absorbent structure.

A demand also exists for absorbent articles for use in managing moisturein prosthetic devices and for delivering drugs to the body which havesimilar properties as those described above, such as suitable fluiduptake, retention and removal, and secure placement and anatomicalconformance with a body.

SUMMARY

The present invention is directed to embodiments of a monolithicabsorbent structure having an apertured facing layer for use in anabsorbent article and methods of making the same.

According to one embodiment, an absorbent structure includes anopen-cell silicone foam having pore walls. In another embodiment, theabsorbent structure may include a closed-cell silicone foam having porewalls. In still another embodiment, the silicone foam is partially aclosed-cell silicone foam having pore walls and partially an open-cellsilicone foam having pore walls.

A plurality of hydrophilic particles is anchored to the pore walls ofthe foam. At least some of the hydrophilic particles have an anchoredportion firmly anchored to the pore walls and an exposed portionextending outwardly away from the pore wall upon which the anchoredportion is anchored.

In one variation of the embodiment, the silicone foam defines opposedfirst and second surfaces. The first surface of the silicone foam hasskin-adherent properties thereby defining a facing layer. The facinglayer of the silicone foam may include a plurality of apertures arrangedin a pattern, and the apertures may have a generally uniform structure.

According to one construction of the absorbent structure, the siliconefoam forms a liquid retention portion within the thickness of thesilicone foam, and a skin-adherent portion underlying the liquidretention portion and generally defined along a first foam surface. Inone variation of this construction, the pore walls of the liquidretention portion may be more cross-linked than the skin-adherentportion of the silicone foam such that the skin-adherent portion istacky to human skin.

By way of example, the hydrophilic particles may amount to being 5%-30%by weight of the total weight of the silicone foam in a dry condition.

Embodiments of the absorbent structure may be provided in an absorbentarticle including the absorbent structure, and a vapor permeable, liquidimpervious backing layer secured to the second surface of the siliconefoam.

The absorbent structure may be made by using the following method:

(1) providing an absorbent powder of 5%-30% of weight of the totalweight of the absorbent structure in a dry condition;

(2) providing a wet powder which is 3% w/w powder in an aqueoussolution;

(3) preparing an uncured mixture including the absorbent powder, the wetpowder and an uncured silicone compound; and

(4) curing the mixture at a predetermined temperature for apredetermined period of time.

Additionally, the method may include the steps of applying the uncuredmixture onto a mold having a plurality of projections arranged in apattern to thereby impart a plurality of apertures on one surface of theabsorbent structure. The mold may also produce an absorbent structurethat can accommodate a device or part of a device, such as by providinga cavity in the absorbent structure.

By heating the mixture, the silicone foam is cross-linked. The curing ofthe mixture may be adapted so that the pore walls of the liquidretention portion are more cross-linked than the skin-adherent portionof the silicone foam. By reducing the degree of cross-linking theskin-adherent portion of the silicone, the skin-adherent portion of thesilicone foam may have an elastomeric consistency so as to minimizetrauma when the absorbent structure is applied over or removed from awound.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a side elevational view showing an embodiment of an absorbentarticle having the absorbent structure.

FIG. 2 is a sectional view corresponding to section A of FIG. 1.

FIG. 3 is a bottom plan view of a variation of the embodiment of theabsorbent article of FIG. 1.

FIG. 4 is a schematic view showing the absorbent article in the form ofan inner sleeve.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

As shown in FIG. 1, a monolithic absorbent structure 10 includes anopen-cell silicone foam 14 having pore walls 18. In the open-cellconfiguration, the pores of the silicone foam are interconnected andcreate an interconnected network of passages throughout the siliconefoam. A plurality of hydrophilic particles 20 are anchored to the porewalls 18 of the open-cell foam 14. The absorbent structure 10 includes afacing layer 12 that defines a plurality of apertures 28 formed alongone of two opposed sides of the absorbent structure 10. The open-cellfoam 14 generally forms a liquid retention portion of the absorbentstructure, whereas the facing layer 12 generally forms a generallyskin-adherent portion. The absorbent structure 10 may also optionallycomprise a backing layer 16.

In an alternate configuration, the silicone foam is a closed-cellsilicone foam. In the closed-cell silicon foam configuration, theaforementioned pores are not connected to each other and thus do notform part of an interconnected network.

In still another configuration, the silicone foam is partially aclosed-cell silicone foam and partially an open-cell silicone foam. Inthis configuration, some of the pores are connected and form aninterconnected network, while some of the pores are not part of anyinterconnected network.

The absorbent structure functions so that as the absorbent structure isplaced on a wound or is exposed to moisture (such as perspiration in aprosthetic device), the moisture is pressed or flows through theapertures of the facing layer and comes into contact with the exposedportions of the hydrophilic particles, which in turn absorb themoisture. Since the silicone foam is generally hydrophobic in nature, itgenerally does not absorb moisture. Instead, the hydrophilic particleslock the moisture in the absorbent structure.

As is well understood, silicone is a hydrophobic material. Embodimentsdescribed herein employ hydrophobic silicones. An exemplary siliconemixture for making the silicone foam comprises MED-4901 manufactured byNuSil Technology, LLC.

The shape and size of the absorbent structure is not limited. Theabsorbent structure may be shaped and sized based on the intendedapplication of the absorbent structure. For example, when used as awound dressing, the absorbent structure may be cut to a size equal to orslightly greater than the wound, such that the wound is covered by theabsorbent structure. In this manner, the absorbent structure serves as abarrier to secondary bacterial infection. As shown in FIG. 4, when usedin a prosthetic device, the absorbent article 10 may be shaped in theform of the inner sleeve 40 of the prosthetic device which comes intocontact with a residual limb where perspiration may form. In thismanner, the absorbent structure serves to move moisture away from theinterface between the residual limb and the prosthetic device, therebyreducing the chance for slippage. When used for drug delivery, theabsorbent structure may be shaped in any size necessary for carrying asuitable amount of drug to be delivered to a targeted area of the body.

In observing FIG. 2, while some of the hydrophilic particles 26 may beembedded and surrounded by silicone in the foam 14, some of thehydrophilic particles 20 have an anchored portion 24 firmly anchored tothe pore walls 18 and an exposed portion 22 extending outwardly awayfrom the pore wall 18 upon which the anchored portion 20 is anchored.The exposed portions 22 enable the hydrophilic particles to take upmoisture while still connecting to the silicone foam and being securedto the foam.

The hydrophilic particles in the silicone foam act to absorb anymoisture brought into the absorbent structure. The hydrophilic particlesfor use in the absorbent structure are described more fully in U.S.application Ser. Nos. 10/725,574 and 11/339,696. The hydrophilicparticles preferably include absorbent powders such as product Z-1069 orFavor PAC 230 from Stockhausen-Degussa Inc.

After absorbing moisture, the hydrophilic particles may retain and storemoisture in the absorbent structure, expel moisture from the absorbentstructure, or both.

The absorbent structure has desirable moisture storage capacity. That isto say, the hydrophilic particles embedded in the absorbent structurehave moisture storage capacity that will provide the absorbent structureof this embodiment with desirable moisture storage capacity. Thehydrophilic particles effectively retain absorbed moisture and areunlikely to allow absorbed moisture to re-enter the environment wherethe moisture originated.

When expelling moisture, the hydrophilic particles expel moisture in theform of vapor. The vapor leaves the particles and moves up through theabsorbent structure towards the surface of the absorbent structureopposing the facing layer. The moisture in the form of vapor eventuallyleaves the absorbent structure, thus allowing the hydrophilic particlesto absorb additional moisture.

According to this embodiment, the hydrophilic particles are generallyspherical. However, the shape of the hydrophilic particles is notlimited to spherical shape. Moreover, hydrophilic fibers may be used inplace of or in conjunction with hydrophilic particles. Hydrophilicfibers suitable for use in the absorbent structure include, but are notlimited to, hydrophilic natural or synthetic fibers.

The hydrophilic particles may be uniformly distributed throughout thesilicone foam. Uniform distribution of the hydrophilic particles helpsto ensure that any expansion of the absorbent article caused by moistureabsorption occurs uniformly throughout the structure. When an absorbentstructure expands in a uniform fashion, the structure is less likely toseparate from the skin outside the wound area due to a “curling” effectmost often caused by uneven swelling of the absorbent structure.

As discussed above, the absorbent structure generally comprises a liquidretention portion and a skin-adherent portion. According to onevariation, the pore walls of the liquid retention portion are morecross-linked than the skin-adherent portion of the silicone foam. Thisresults in the skin-adherent portion having an elastomeric form with atackiness that lends itself to being skin adherent. The elastomeric skinadherent portion has a soft, gel-like feel. This provides the addedbenefit, as in the facing layer of U.S. patent application Ser. No.10/725,574, of gently securing to a wound or skin and allowing theabsorbent structure to be gently removed therefrom. The ability togently remove the absorbent structure from a wound both reduces the painto a patient and also decreases the risk of traumatizing the woundduring removal.

As discussed above, the absorbent structure may comprise a backing layerformed on the surface opposing the facing layer. The backing layer maybe a vapor permeable, liquid impervious backing layer. Exemplary backinglayers and methods for securing the same onto the absorbent structureare described in U.S. applications No. 10/725,574 and 11/339,696 thatare incorporated herein by reference, and owned by the assignee of thepending application.

By providing a vapor permeable backing layer, the absorbent structure isstill capable of expelling moisture from the absorbent structure in theform of vapor as discussed above. A vapor permeable backing layer allowsmoisture in the form of vapor to escape the absorbent structure. Themoisture storage capacity of the absorbent structure is increased whenthe hydrophilic particles continually release moisture in the form ofvapor that passes out of the absorbent structure.

It will be noted that the backing layer may be any type of layer whichprovides desirable characteristics such as being vapor permeable orimpermeable. The backing layer may comprise layers other than films, andmay be a textile such as a stretchable knit material or unbroken loopmaterial. The absorbent structure may be secured to such backing layersby lamination, adhesives or may be coated directed onto the surface ofthe backing layer. In addition, the backing layer may be a silicone orother polymeric sheet that is either or not vapor permeable. In suchpolymeric sheet, the sheet may provide structural reinforcement, such asby its thickness or reinforcement by a textile or other suitablematerial, to the silicone foam.

As exemplified in FIGS. 1 and 3, the absorbent structure 10 includes afacing layer 12 that defines a plurality of apertures 28 formed andmolded along one of two opposed surfaces of the absorbent structure 10.The apertures 28 may be formed in a variety of patterns andconfigurations, as demonstrated in FIG. 3 wherein there is an aperturedregion 30 and a non-apertured region 32 formed along the surface of theabsorbent structure. The apertures may be formed in any of theconfigurations described in U.S. application Ser. No. 10/725,574.

In addition to molding the absorbent structure to comprise a pluralityof apertures, the absorbent structure may also be molded such that itcan accommodate devices or a portion of a device. For example, theabsorbent structure may be molded to include a cavity in to which adevice or a portion of a device may be inserted.

In another embodiment, a method of making the absorbent structure isdisclosed. The method includes the step of providing an absorbent powderof 5%-30% of weight of the total weight of the absorbent structure in adry condition. A wet powder is provided with about 3% w/w powder inwater so as to make it easier to add water for making the foam. Anuncured silicone mixture comprising part A and part B of MED-4901 fromNuSil Technology, LLC in a ratio of 1:1 is mixed with the absorbentpowder and the wet powder. The mixture is cured at a temperature in therange of 150° C.-200° C. for about 10 minutes. At the end of curing, afoam is formed with the absorbent powder.

In another method for making the absorbent structure, the methodincludes the step of providing an absorbent powder of 5%-30% of weightof the total weight of the absorbent structure in a dry condition. A wetpowder is provided with about 3% w/w powder in water so as to make iteasier to add water to the eventual mixture for making the foam. Anuncured silicone mixture is mixed with the absorbent powder and the wetpowder. The mixture is cured at a temperature at about 100° C. for about15-20 minutes. At the end of curing, a foam is formed with the absorbentpowder.

In these methods, the silicone is foamed due to the introduction ofwater and the high curing temperatures, as is well understood by oneskilled in the art. The water evaporates during the curing of thesilicone, and the absorbent powder is evenly distributed in the foamstructure so as to render the resultant absorbent structure partiallyhydrophilic without substantially changing the functional groups of thesilicone itself. The even distribution of the powder in the absorbentstructure also provides the absorbent structure with the benefitsdescribed above in the previous embodiment.

The method of this embodiment may further comprise the step of applyingthe uncured mixture onto a mold having a plurality of projectionsarranged in a pattern. The curing step is performed after the uncuredmixture is placed in the mold, thereby resulting in an absorbentstructure having the shape of the mold once the curing step has beenperformed. Any curing method well known to those of ordinary skill inthe art may be used in this embodiment.

The projections in the mold impart a plurality of apertures on onesurface of the absorbent structure. As discussed in the previousembodiment, the pattern and configurations of the projections in themold can be any variety of patterns and configurations, thus making themethod described herein capable of producing an absorbent structurehaving apertures in a variety of patterns and configurations.

The method of this invention may also employ a mold which, after curing,produces an absorbent structure that can accommodate devices or portionsof devices as described in the previous embodiment.

A step of securing a vapor permeable, liquid impervious backing layer onone surface of the absorbent structure may also be included in themethod of this embodiment. The backing layer is preferably secured tothe surface of the absorbent structure opposed to the facing layerhaving apertures. The backing layer may be secured to the absorbentstructure by any means known in the art, including those methodsdescribed in U.S. application Ser. Nos. 10/725,574 and 11/339,696.

The silicone foam undergoes cross-linking during the curing step. Thatis to say, application of heat causes the silicone mixture tocross-link. In a preferred configuration, the curing step is performedsuch that the pore walls of the liquid retention portion of theabsorbent structure are more cross-linked than the skin-adherent portionof the silicone foam. This results in the skin-adherent portion havingan elastomeric form with a tackiness that lends itself to being skinadherent. The elastomeric skin adherent portion has a soft, gel-likefeel.

It will be understood that the above described embodiments and methodsof the invention are illustrative in nature, and that modificationsthereof may occur to those skilled in the art. Accordingly, thisinvention is not to be regarded as limited to the embodiments disclosedherein, but is to be limited only as defined in the appended claims.

1. An absorbent structure for a prosthetic device comprising: a poroussubstrate in the form of an inner sleeve and having pore walls; and aplurality of hydrophilic particles anchored to the pore walls of theporous substrate, wherein a portion of the plurality of the hydrophilicparticles have an anchored portion anchored to the pore walls and anexposed portion extending outwardly away from the pore wall upon whichthe anchored portion is anchored.
 2. The absorbent article according toclaim 1, wherein the porous substrate defines opposed first and secondsurfaces, the first surface of the porous substrate having skin-adherentproperties.
 3. The absorbent article according to claim 2, wherein avapor permeable, liquid impervious backing layer is secured to thesecond surface of the porous substrate.
 4. The absorbent articleaccording to claim 1, wherein the porous substrate has opposed first andsecond surfaces, the porous substrate forming a liquid retention portionwithin the thickness of the porous substrate, and a skin-adherentportion underlying the liquid retention portion and generally definedalong the first surface of the porous substrate.
 5. The absorbentarticle according to claim 4, wherein the porous substrate is across-linked polymer, the liquid retention portion being morecross-linked than the skin-adherent portion of the porous substrate. 6.The absorbent article according to claim 2, wherein the first surfacedefines a plurality of generally uniformly spaced and formed holes, theabsorbent structure being monolithic.
 7. An absorbent structurecomprising: a hydrophobic, polymeric porous substrate; and a pluralityof hydrophilic particles anchored to the pore walls of the poroussubstrate, wherein a portion of the plurality of the hydrophilicparticles have an anchored portion anchored to the pore walls and anexposed portion extending outwardly away from the pore wall upon whichthe anchored portion is anchored.
 8. The absorbent structure accordingto claim 7, wherein the porous substrate defines opposed first andsecond surfaces, the first surface of the porous substrate havingskin-adherent properties.
 9. The absorbent structure according to claim8, wherein a vapor permeable, liquid impervious backing layer is securedto the second surface of the porous substrate.
 10. The absorbentstructure according to claim 7, wherein the porous substrate has opposedfirst and second surfaces, the porous substrate forming a liquidretention portion within the thickness of the porous substrate, and askin-adherent portion underlying the liquid retention portion andgenerally defined along the first surface of the porous substrate. 11.The absorbent structure according to claim 10, wherein the poroussubstrate is cross-linked, the liquid retention portion being morecross-linked than the skin-adherent portion of the porous substrate. 12.An absorbent structure comprising: a hydrophobic silicone poroussubstrate including a plurality of internal walls; and a plurality ofhydrophilic particles anchored to the pore walls of the siliconesubstrate, wherein a portion of the plurality of the hydrophilicparticles have an anchored portion anchored to the internal walls and anexposed portion extending outwardly away from the internal walls uponwhich the anchored portions are anchored.
 13. The absorbent structureaccording to claim 12, wherein the silicone substrate defines opposedfirst and second surfaces, the first surface of the silicone substratehaving skin-adherent properties.
 14. The absorbent structure accordingto claim 13, wherein the first surface defines a plurality of generallyuniformly spaced and formed holes, the absorbent structure beingmonolithic.
 15. The absorbent structure according to claim 12, whereinthe silicone substrate has opposed first and second surfaces, thesilicone substrate forming a liquid retention portion within thethickness of the silicone substrate, and a skin-adherent portionunderlying the liquid retention portion and generally defined along thefirst surface of the silicone substrate.